The present invention relates to motor controllers and more specifically to methods and systems for identifying system inertia and load torque disturbances that are needed to properly tune motor controllers.
As well known in the motor control industry, motor/plant inertia identification is an important step in properly tuning a motor drive system. To this end, the way a motor and a linked load (i.e., the plant) respond to control signals (i.e., applied varying voltages) is directly related to motor/plant inertia and therefore, suitable control is directly related to plant inertia. One way to determine plant inertia has been to perform an inertia determining commissioning process prior to normal motor operation and then setting and assuming a constant system inertia value. While these processes work well, they have at least two primary shortcomings.
First, commissioning processes take time to complete and therefore slow the process of setting up a control/drive system. A related issue is that, typically, a skilled engineer or technician is required to properly perform a commissioning procedure and therefore there are costs associated with each additional commissioning step required to set up a drive system.
Second, in at least some applications system inertia changes during system operations. Where inertia changes during operation, the assumed constant value is erroneous and therefore drive control is less than optimal.
One solution in the case of a system where inertia changes during operation is to routinely rerun the inertia estimating commissioning procedure (e.g., once a day). This solution, however, increases the time required to maintain an accurate estimate and does not work well where system inertia fluctuates during the interim periods between recalculation.